Untangling Complexity in ASEAN Air Traffic Management through Time-Varying Queuing Models

Round 1

Reviewer 1 Report

This paper provides a detailed review of the research efforts made by the authors. The research topic is relevant and it is adequately addressed from both, industry and academic viewpoints. Given that the content reviewed seems good for journal publication, in continuation I’m listing a few recommendations which may contribute to its better presentation.

Since a significant part of content refers to previous research findings it is advised to place such content under a specific title named “Research Background” and place it just after the Introduction part. In that context, graphical representations should be (firstly) referenced within content and then displayed (and not vice versa). In addition, too many times the term “target FIR” is used, whereby that term can be replaced with FIR’s actual name. Speaking of terms meaning, the terms “optimal” and “ideal”, used in a way like e.g., “ideal air traffic patterns”, have contextual meaning. Hence, it is advised to acknowledge more clearly how or in what respect the optimality/ideality is determined. Furthermore, since the paper introduces a lot of methodological assumptions, most of which are based on real-world scenarios, it is suggested to reason assumptions introduced with pieces of evidence derived from literature review or other sources.

Overall, the aim, research hypothesis and the original contribution of the research paper reviewed are clearly presented and further elaborated. Also, the methodology used is well documented. However, in according with best practice, it is advised to list the research hypothesis in the introductory part of the paper. Last but not least, while the most of literature is cited within the Introduction, the literature review should be more extensive and placed up also with respect content presented within the Discussion - speaking of which, it should be more focused on results obtained rather than on future work aspirations.

The spelling and terminology used are adequate, but they can be further improved by making sentences a bit shorter, by replacing wording like “a dramatic increase” with something like “a significant increase”, by reducing title length of figures and tables and by avoid referencing your previous work in a following style “our past work…; We also ran…; we are convinced(?)" etc. (in general try to use neutral language to express your contribution without exactly expressing it) by using more indirect phrases like “the previous work points out … literature review indicates …”. Also, it is recommended to avoid direct referencing of “the authors’ past research” within the Abstract.

Author Response

Dear reviewer,

Thank you very much for through review and constructive comments. We carefully read all comments and revised the paper. Please find our answers to your comments as follows.

[Answers]

• As you pointed out, our introduction includes research backgrounds and literature citations. We considered placing the backgrounds in an independent chapter after the introduction, but it made significantly difficult to explain the purpose of this paper. Thus, instead of replacing the background in an independent chapter, editorial efforts were made following your comments. We believe that the readability is improved in the introduction chapter despite separating research background from the introduction.
• According to your comments, we modified the entire paper without using the terms of “target FIR”.
• We clarified the meaning of terms “ideal”, “optimal”, and “ideal traffic patterns” in the revised paper. As newly explained at the end of the 4^th paragraph in the introduction, “ideal traffic pattern” reduces potential hotspots and relieving the air traffic complexity.
• Indeed, this paper introduces a lot of methodological assumptions in ASEAN airspaces. As you pointed out, it is the best to refer official documents to explain the real-world scenarios, but these documents are very less and disclosed. Additionally, we are limited to publish this information due to governmental policies. For supplying the less literature and sources, we made efforts to revise Chapter 2, and tried to explain the operational assumptions. We believe that this paper will provide useful sources and knowledge to future academic publications on the ASEAN air traffic management.
• The hypothesis is that application of a time-varying fluid queuing model reduces the potential conflicts. Under the hypothesis, we also listed out our approaches in the 5^th We believe the editorial efforts improved readability in this paper.
• This paper presents a novel conceptual queue-based approach, which enable us to interplay functions that ASEAN partners would have to consider when introducing FRA. According to the novelty (on both an approach and operation in the ASEAN region), literature to refer in the discussion chapter are very limited. We made effort to clarify the contribution of the obtained results in this paper at the beginning of the discussion chapter. Furthermore, we enriched the summary of the obtained results in the conclusion chapter.
• All sentences were made to be shorter in the entire manuscript.
• We modified to use indirect phases to point out our past works.
• We deleted the direct referencing of the authors’ past research in the abstract.
• Graphical configuration will be carefully addressed in the proofreading process.

Reviewer 2 Report

Dear authors,

I was invited to review your paper titled "Untangling Complexity in ASEAN Air Traffic Management through Time-varying Queuing Models". The paper addresses a relevant topic in air transportation/ATM research. Reducing complexity/workload. The paper follows a clear train of thought and applies it to an interesting use case. The combination of queuing model and fast-time simulation provides tangible results to demonstrate the conceptual approach.

In its entirety this is a good paper. Thus, my enclosed comments represent observations on a high level with a view to help improve the paper.

One of the key take-aways I want to convey to you is to cross-check your use of long sentences, conditional constructions, and combining messages. In many instances this puts quite some strain on the reader to follow through. Thus, you are losing out on your engaging writing style - in my view.

Good luck with the finalisation of the draft.

Comments for author File: Comments.pdf

Aside from a few spelling errors, the draft is well written. However, many sentences take on a very long form and combine messages/statements that can be better packed into 2 different sentences. As a rule of thumb, shorten your sentences to span not more than 1.5-2 lines. Be even more ruthless in the abstract. Think about simplifying your phrases and sentence structure. This will help to reduce the cognitive load on the reader. Your style is engaging and I think you loose out by leaning towards over-complicating sentence constructions.

Author Response

Dear reviewer,

Thank you very much for your thorough review and kind support to improving the paper. We carefully read all of your comments and revised paper. Please find our answers to the comments as follows.

[Answers to the general comments]

- We cross-checked the use of long sentences, conditional constructions, and combining messages, and improved readability of the manuscript.

- Spelling errors were modified.

- We made editorial efforts to shorten most of sentences to span no more than 1.5-2.0 sentence structure.

[Answers to the specific comments on the peer review report]

Paper Overview

- According to your suggestions, we revised to keep sentences shorter and breaking the messages in separate sentences, and tried to eliminate some filler words and phrases. We believe that the revised paper improved the readability.

Abstract

- According to your comments, we cleaned up entire abstract and clarified the scope of this paper. All sentences are shortened to maximally 1.5 lines of the abstract.

1.Introduction

- We explained what was meant with “hotspot”. For avoiding any confuse, we deleted the description “target airspace”, where the paper focused to control traffic. Contribution of our work was highlighted at the end of the introduction section.

2.En-route Trajectory Complexity in the FIR

- We explained why direct-to from entry to exit represents a fair assumption of FRA.

- All sentences were restricted for clarity.

- In the submitted version we failed to clearly explain that the main purpose of adding the longitudinal time spacing was (1) to improve the realism of the departure time interval pattern based on how real operations happens, and (2) to remove in simulation false potential conflicts that do not happen because they present unnecessary noise in the study. The false potential conflicts were results of insufficiency of the reference simulation, which had the focus on regional application. We noticed that the reference simulation contained such false potential conflicts, and rectified.

- The reason of cluster selection was given in two parts: in the main text in chapter 2.2, and in the additional texts in the legend of Table 2.

3.Interpretation of complexity

- A time-varying queuing model represents time-varying air traffic volume at an assigned area. The queuing network model represents air traffic complexity through multiple queuing models. We explained these points clearly in the beginning of the chapter 2. Additionally, we edited the paragraph for avoiding any redundancies.

3.2 Modeling Air Traffic Queues in the Hotspot

- According to your suggestion, we enriched explanations on how Fig.5 support ATCo comments and operational analysis in the 4^th paragraph in Chapter 3.2. We estimated TVs using aircraft arrival rates every 5 minutes. We believe that 5 minutes is relevant in terms of application for departure time controls in this paper.

4. Untangling the Complexity in ATM

- On the allocation of Fig. 7, 8, 9, we will take care on the proofreading process. Following your example, we explained how to read Fig. 8 comparing with Fig. 5 in the third paragraph in Chapter 4.1.

- Thanks to your constructive comments, we improved the last paragraph in Chapter 4.1. Here we justified that departure time control brought down the complexity below a certain value.

4.2 Effectiveness of the Departure Air Traffic Flow Control

- We improved two sentences you mentioned.

- Thank you very much for your insightful comments on the contribution of our work. Based on your comment, we addressed the contribution to the ASEAN partners in the first paragraph of the discussion in Chapter 5.

5. Discussion

- The title of Chapter 5.1 was changed to “Balancing local effects in the wider regional network”.

- This paper focused on departure time control because the C80 hotspot was highly impacted by WSSS/WMKK departures. Speaking of balancing the hotspot deconfliction, the other potential could be controlling arrival traffic flow strategically. Based on your comment, further discussion was given this in Chapter 5.2.

- Spelling typo/phrase was modified.

6. Conclusion

- According to your comments, we edit conclusion section to summarize the achievement in this paper clearly.

Editorial comments

- Thank you very much for your careful reviews and editorial supports. We carefully read all of your comments and modified the paper following them. We believe that the quality of the paper is improved by clarifying all points you mentioned.

Reviewer 3 Report

A time-varying Fluid Queuing model has been developed for analysis of traffic flows in a particular hotspot area in ASEAN airspace in a Free Route Airspace concept. The application of the time-varying Fluid Queuing model in air traffic management is not new, for instance two of the authors presented its application in Aerospace 9(3) (2022) for departure modelling. While the application of a queuing model for a runway departure process is a sensible approach, since a runway can be seen as a single server, the authors have failed to clarify why a queuing modelling approach is sensible for effective analysis of an en-route hotspot area.

Following analysis of service times in a particular hotspot area C80 basically 13 traffic flows were identified, which were modelled by 13 Fluid Queues. Next following feedback of air traffic controllers (the approach to attain this feedback is not explained), it is considered that coincidence of some of these flows are problematic and some are not. Next the identified problematic flows are segregated to a particular extent by departure delays. Depending on the setting this leads to average delays of more than 3 hours, of about half an hour, or of about 16 to 19 minutes (see Table 2). It follows from Figure 10 that time constraints between departures at an airport could not be included in the queuing model, such that they had to be added separately. It follows from a fast-time simulation using AirTop that the application of the queuing model did not effectively reduce the number of conflicts and that the numbers of conflicts outside of the considered hotspot area were increased (Table 4).

In conclusion the application of the Fluid Queuing model is not novel for ATM, it leads to operationally unacceptable results for this en-route use case, and it does not sufficiently address the possible approaches by air traffic controllers for handling complexity in en-route sectors.  

No comments.

Author Response

Dear reviewer,

Thank you very much for through review and comments. We carefully read all of your comments and revised the paper. Please find our answers as follows.

[Answers]

• In this paper, time-varying fluid queue was used to estimate the time varying amount (volume) of aircraft crossing the hotspot area. Our model was developed not to define the number of servers in the en-route airspace. At the beginning of Chapter 3, we made editorial efforts to clearly explain how we model the air traffic applying the fluid queue and queuing networks to the air traffic in en-route airspace. We believe that clear explanations of the use of queuing models resolve your concern.
• We believe that our conceptual approach contributes to design the interplay of functions that ASEAN partners would have to consider when introducing FRA operation. The results justified that Air Traffic Flow Management (ATFM) functions could be addressed to realize better Air Traffic Service (ATS) provision. These contributions were clarified in the revised manuscript.

Round 2

Reviewer 3 Report

Thank you for your clarifications. 

I understand that the time-varying fluid queue was used to estimate the time varying amount (volume) of aircraft crossing the hotspot area. However it remains vague how the approach can be used effectively, considering the large delays, the lack of representation of time constraints at the airport, and the lack of effective reduction of conflicts, including the introduction of conflicts outside of the hotspot area. So my expectation is that other methods will be essential to support the analysis of the impact of FRA in the ASEAN airspace. 

None